What is the optional 220.82 method?

NEC 220.82 is a simplified optional calculation for a single dwelling served by one 120/240 V or 120/208 V service. It applies a 3 VA per square foot general load plus appliance nameplates, demands the first 10 kVA at 100 percent and the remainder at 40 percent, then adds the larger of the air-conditioning or heating load.

Why is the first 10 kVA treated differently?

NEC 220.82(B) recognizes that not every general load and appliance runs at once. It counts the first 10 kVA of general load at full value, then only 40 percent of the remainder, reflecting realistic diversity so the service is not grossly oversized.

How are heating and cooling handled?

NEC 220.82(C) lets you take only the largest of several heating and cooling scenarios because a home rarely heats and cools at the same time. This tool simplifies that to the larger of the air-conditioning load or the electric space-heating load at 100 percent.

Do appliance watts equal VA?

For resistive appliances like water heaters, ranges, and baseboard heat, watts and VA are effectively equal, so you can enter nameplate watts directly. For motor-driven equipment the VA is slightly higher than the watts, so use the nameplate VA or volt-amp rating when available.

Does the result account for conductor ampacity?

No, it gives the minimum service ampacity from the load. You still must size the service-entrance conductors from the ampacity tables and verify the chosen service size with your authority having jurisdiction before finalizing.

What is the Service Load Calculation (NEC 220)?

Walks through the NEC 220.82 optional residential method, applying 3 VA per square foot lighting, small-appliance and laundry circuits, appliance nameplates with the first-10-kVA-at-100-percent demand, plus the larger of AC or heat, to find the minimum service ampacity. For electricians on permits and service upgrades. It runs free in your browser on Gera Tools, with nothing uploaded.

Service Load Calculation (NEC 220)

Name: Service Load Calculation (NEC 220)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

Get one useful tool a week

Like this tool? Enter your email and we'll send you one genuinely useful Gera tool a week — plus a link to come back to this one. No spam, one-click unsubscribe any time.

Sizing a home’s electrical service is a permit requirement and the foundation of any panel upgrade. The NEC 220.82 optional method is the most common residential calculation; this tool runs it end to end and returns the minimum service size.

How it works

General loads are summed and demanded, then the larger HVAC load is added at full value:

general  = 3 × ft² + 1500 × small-appliance circuits + 1500 × laundry + appliances
demand   = general ≤ 10000 ? general : 10000 + (general − 10000) × 0.40
hvac     = max(air-conditioning, electric heat)
total VA = demand + hvac
amps     = total VA / service voltage (240 or 208)

The first 10 kVA of general load counts fully, the rest at 40 percent, reflecting that not everything runs at once.

Detailed worked example

A 2,000 ft² home with:

Two small-appliance circuits (kitchen)
One laundry circuit
Fastened appliances totaling 18 kVA (range 12 kVA, water heater 4.5 kVA, dryer 5.5 kVA — note: these overlap but enter the nameplate total)
Air conditioning: 5 kVA
Electric space heating: 9 kVA

Step 1 — General load:

3 VA × 2,000 ft² = 6,000 VA
Small appliance: 2 × 1,500 = 3,000 VA
Laundry: 1 × 1,500 = 1,500 VA
Appliances: 18,000 VA
General subtotal = 28,500 VA

Step 2 — Demand factor:

First 10,000 VA at 100% = 10,000 VA
Remaining 18,500 VA at 40% = 7,400 VA
Demanded load = 17,400 VA

Step 3 — HVAC:

Larger of AC (5 kVA) or heat (9 kVA) = 9,000 VA

Step 4 — Total and service size:

Total VA = 17,400 + 9,000 = 26,400 VA
Amps = 26,400 / 240 = 110 A → minimum 125 A service

What the 40 percent demand factor reflects

The 40% factor on general loads above 10 kVA acknowledges that residential wiring is sized for simultaneous use of every circuit at full rated load — but that never actually happens. The diversity factor captures the statistical reality that even in a fully occupied home, the combined actual draw on general lighting, outlet, and appliance circuits is a fraction of the theoretical maximum. Without a demand factor, a 4,000 ft² home would calculate to an impractically oversized service.

When to use the standard method instead

The NEC 220.82 optional method is only valid for a single dwelling unit served by a single service. It is not valid for:

Multi-family buildings
Commercial premises
Three-phase services
Unusual load compositions that the demand factor assumptions do not cover

For those cases, NEC 220.42 through 220.53 provides the standard calculation with specific demand factors per load type.

Notes

Always confirm the result with the standard method when loads are unusual, and size the service conductors from the ampacity tables rather than the bare amp figure here. The minimum service ampacity from the load calculation is the starting point; standard service sizes are 100, 125, 150, 200, 320, and 400 amperes. Select the next standard size above the calculated minimum.